Chronic myelogenous leukemia (CML) is characterized by the presence of the chimeric p210bcr-abl protein which shows elevated protein tyrosine kinase activity relative to the normal c-abl tyrosine kinase. Although many of the p210bcr-abl substrates have now been identified, the relevance of these phosphorylation events in the pathogenesis of CML and the normal function of these p210bcr-abl substrates and are still poorly understood. The focus of this proposal is to elucidate, in vivo in the mouse, the functions of three p210bcr-abl phosphorylation targets, Dok1, 2 and 3, and to determine how these relate to the pathogenesis of CML by a direct genetic approach with the following Specific Aims: 1) To define, in single knock out mice and null cells, the role of Dok1, 2, 3 in ontogenesis and hemopoiesis. We have disrupted the Dok 1, 2, 3 genes and mice lacking their functions (-/-, null) have been generated. Ontogenesis and hemopoiesis will be studied in these mutants. 2) To define in double or triple knock-out mutants the role of Dok1, 2, 3 in ontogenesis and hemopoiesis. We will intercross the various Dok-/- mice among them in order to generate double or triple knock-out mutants. We will define the developmental role of these genes and their role in hemopoiesis by characterizing the embryonic and adult phenotype resulting from their concomitant inactivation. 3) To establish the role of Dok proteins in leukemia and cancer promotion/progression. We will examine spontaneous or physically/chemically induced tumorigenesis as well as leukemogenesis by p210bcr-abl in the various K.O. mutants and in double and triple Dok-/- mutants. We will cross Dok1-/- mutants with mice lacking Nf1 or Pten gone products to test whether Dok1 cooperates with these proteins in tumor suppression. 4) To identify genes critical for Dok1, 2 and 3 function and for CML pathogenesis. We will utilize purified cell populations from our single, double and triple K.O. mutants to identify, on a comparative basis, target genes relevant for their function. We will test whether these genes are also deregulated in CML blasts.